After missing the last train following a company drinking party, new employee Sayu ends up staying over at the protagonist's place, using the excuse that his wife is away at her parents' house. Shortly after arriving, Sayu falls asleep, and unable to resist, he inserts himself into her while she remains unconscious. Later, Sayu suddenly visits again on a weekend, playfully threatening to expose what happened that night, teasing him with a mischievous, devilish attitude. The story gradually unfolds their deepening relationship beyond the office.